15 vs 12 is huge gap in relative age, development, and maturity. But it sounds worse from your description, like a 15yo can have sex with a 10yo and it's considered consensual??
It is _now_ that a 15yro and a 10yro _may_ be considered consensual if no other factors come into play, like authority. However, the court would have to examine it on a case-by-case basis.
Previously, it was _assumed_ that consent occurred. Such as in the case I pointed out - the court struggled to say there was not willing engagement between a 28 yro and an 11 yro.
Historically speaking, France has some of the loosest laws around consent in the world.